THE ROLE OF DYNAMIC 3-DIMENSIONAL TRUNK MOTION IN OCCUPATIONALLY-RELATED LOW-BACK DISORDERS - THE EFFECTS OF WORKPLACE FACTORS, TRUNK POSITION, AND TRUNK MOTION CHARACTERISTICS ON RISK OF INJURY

Current ergonomic techniques for controlling the risk of occupationall y-related low back disorder consist of static assessments of spinal lo ading during lifting activities. This may be problematic because sever al biomechanical models and epidemiologic studies suggest that the dyn amic characteristics of a lift increase spine loading and the risk of occupational low back disorder. It has been difficult to include this motion information in workplace assessments because the speed at which trunk motion becomes dangerous has not been determined. An in vivo st udy was performed to assess the contribution of three-dimensional dyna mic trunk motions to the risk of low back disorder during occupational lifting in industry. More than 400 repetitive industrial lifting jobs were studied in 48 varied industries. Existing medical and injury rec ords in these industries were examined so that specific jobs historica lly categorized as either high-risk or low-risk for reported occupatio nally-related low back disorder could be identified. A triaxial electr ogoniometer was worn by workers and documented the three-dimensional a ngular position, velocity, and acceleration characteristics of the lum bar spine while workers lifted in these high-risk or low-risk jobs. Wo rkplace and individual characteristics were also documented for each o f the repetitive lifting tasks. A multiple logistic regression model w as developed, based on biomechanical plausibility, and indicated that a combination of five trunk motion and workplace factors distinguished between high and low risk of occupationally-related low back disorder risk well (odds ratio: 10.7). These factors included 1) lifting frequ ency, 2) load moment, 3) trunk lateral velocity, 4) trunk twisting vel ocity, and 5) the trunk sagittal angle. This analysis implies that by suitably varying these five factors observed during the lift collectiv ely, the odds of high-risk group membership may decrease by almost 11 times. The predictive power of this model was found to be more than th ree times greater than that of current lifting guidelines. This study, though not proving causality, indicates an association between the bi omechanical factors and low back disorder risk. This model could be us ed as a quantitative, objective measure to design the workplace so tha t the risk of occupationally-related low back disorder is minimized.